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1
Wright, Patricia Ann. "Understanding MS/MS fragmentation pathways of small molecular weight molecules". Thesis, University of Greenwich, 2015. http://gala.gre.ac.uk/18134/.
Testo completoAbstract (sommario):
Fragmentation of molecules by collision-induced dissociation (CID) is not well-understood, making interpretation of MS/MS spectra difficult and limiting the effectiveness of software tools intended to aid mass spectral interpretation. An approach is required which is tailored to each individual molecule and improves the ‘chemical sense’ of the software. It was hypothesised that the bonds which break during CID of protonated molecules are the bonds which are elongated, and hence weakened, as a result of conformational changes induced by protonation. Bond length changes for a test set of molecules were calculated using quantum chemistry software. Density Functional Theory (DFT) or Austin Model 1 (AM1) or both were used to energy minimise the structures of the neutral molecules and their corresponding protonated molecules (protonated at all possible sites). Bonds which elongated to the greatest extent after protonation were compared to the bonds which were found to cleave to give the product ions in the CID spectra of these compounds. Quantum chemistry modelling was also applied to the deprotonated molecules. AM1 calculated bond lengths were found to be similar to those generated by DFT and have the advantage of being rapidly obtained. All the polarised bonds which cleaved were calculated to elongate significantly, thus achieving a 100% success rate in the prediction of bond cleavage as a result of protonation on a heteroatom. The proton is mobile across the molecule, leading to fragmentation when the proton reaches a site where it causes significant bond elongation, provided the molecule has sufficient internal energy. Cleavage of carbon-carbon bonds was not predicted. The success rate for predicting bond cleavage in deprotonated molecules was 48%, suggesting this approach cannot be applied reliably for these anions. AM1 calculated bond length change acts as a descriptor for predicting polarised bond cleavage in protonated pseudo-molecular ions having the potential to be incorporated in mass spectral interpretive software to increase the accuracy of prediction of CID spectra.
2
Nightingale, Philip D. "Low molecular weight halocarbons in seawater". Thesis, University of East Anglia, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280971.
Testo completo
3
Waters, Benjamin Ragan. "Molecular weight modulation in polyhydroxybutyrate fermentations". Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/38974.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, June 2007.Includes bibliographical references.
Polyhydroxybutyrate (PHB) is a material with significant potential for commercial applications. It has material properties similar to isotactic polypropylene; it can be produced from renewable resources; it is biodegradable. Unfortunately, it is very brittle when compared to polypropylene. The physical property that most significantly affects elastic behavior is molecular weight. In an effort to understand how molecular weight is formed in PHB production, kinetic studies of PHB fermentations have been performed using fermentation conditions which allow biomass growth and PHB production phases to be separated. These data indicate that molecular weight increases very quickly and then remains fairly constant in PHB fermentations. Additional studies have indicated that only slight changes in molecular weight can be caused by changing fermentation process conditions or using mutants of the polymerization enzyme. Additionally, one mutant polymerization enzyme has been shown to excrete moderate levels of PHB monomer, 3-hydroxybutyrate, into the fermentation media. This may have application in achieving synthetic production of PHB.
by Benjamin Ragan Waters.
Ph.D.
4
Li, Melissa. "A microscale molecular weight analysis method for characterizing polymers solutions of unknown concentrations". Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/31673.
Testo completoAbstract (sommario):
Thesis (M. S.)--Biomedical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Hang Lu; Committee Co-Chair: Rachel Chen; Committee Member: Johnna Temenoff; Committee Member: Yonathan Thio. Part of the SMARTech Electronic Thesis and Dissertation Collection.
5
Aktaş, Ece. "Low-Molecular Weight Molecules as Selective Contacts for Perovskite Solar Cells". Doctoral thesis, Universitat Rovira i Virgili, 2021. http://hdl.handle.net/10803/672777.
Testo completoAbstract (sommario):
La tecnologia fotovoltaica és una de les fonts d'energia neta i renovable més prometedores per reduir l'impacte ambiental dels combustibles fòssils en les últimes dècades. en aquest context, les perovskites són un material que ha atret recentment una atenció important a causa de la seva capacitat per aconseguir eficiències de conversió molt elevades. Les capes de càrrega selectiva juguen un paper crucial en el ràpid augment del rendiment del dispositiu i en l'estabilitat de les cel·les solars de perovskita. Recentment, l'aplicació de mono-capes auto-assemblades formades per molècules orgàniques que funcionen com a capes selectives de càrrega en cel·les solars de perovskita ha atret una gran atenció a causa d'avantatges com la rendibilitat, l'estabilitat i l'absència d'additius. L'objectiu d'aquesta tesi és el disseny i la síntesi de noves molècules que formen mono-capes auto-assemblades que funcionin com a capes selectives de forats en cel·les solars de perovskita per aconseguir una eficiència de conversió d'alta d'energia i una vida d'envelliment d'alt rendiment feta a mida.La tecnología fotovoltaica es una de las fuentes de energía limpia y renovable más prometedoras para reducir el impacto ambiental de los combustibles fósiles en las últimas décadas. en este contexto, las *perovskites son un material que ha atraído recientemente una atención importante a causa de su capacidad para conseguir eficiencias de conversión muy elevadas. Las capas de carga selectiva juegan un papel crucial en el rápido aumento del rendimiento del dispositivo y en la estabilidad de las celdas solares de *perovskita. Recientemente, la aplicación de *mono-capes auto-asemejadas formadas por moléculas orgánicas que funcionan como capas selectivas de carga en celdas solares de *perovskita ha atraído una gran atención a causa de ventajas como la rentabilidad, la estabilidad y la ausencia de aditivos. El objetivo de esta tesis es el diseño y la síntesis de nuevas moléculas que forman *mono-capes auto-asemejadas que funcionen como capas selectivas de agujeros en celdas solares de *perovskita para conseguir una eficiencia de conversión de alta de energía y una vida de envejecimiento de alto rendimiento hecha a medida.
Photovoltaic technology is one of the most promising clean and renewable energy sources to reduce the environmental impact of fossil fuels in recent decades. In this context, perovskites are a material that has recently attracted significant attention due to their ability to achieve very high conversion efficiencys. Selective charge layers play a crucial role in rapidly increasing device performance and in the stability of perovskite solar cells. Recently, the application of self-assembly mono-caps made up of organic molecules that function as selective layers of charge in solar perovskite cells has attracted great attention due to advantages such as profitability, stability and the absence of additives. The goal of this thesis is the design and synthesis of new molecules that form self-assembly mono-layers that function as selective layers of holes in solar perovskite cells to achieve high-energy conversion efficiency and a high-performance aging life tailored to size.
6
Adebekun, Aderinola Kolawole. "On-line control of molecular weight distribution". Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/12039.
Testo completo
7
Hui, Yu 1977. "Heterjunctions of small molecular weight organic semiconductors". Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=81540.
Testo completoAbstract (sommario):
Photodiodes made of small molecular weight organic semiconductors have been fabricated. The organic materials under investigation are p-type Copper phthalocyanine (CuPc) and n-type 3,4,9,10-perylenetetracarboxylic bisbenzimidazole (PTCBI). Current-voltage and capacitance-voltage measurements have been performed to evaluate the electrical properties of the organic photodiodes. Optical measurements including responsivity and temporal response have also been carried out. It has been found that device efficiency of the photodiodes is influenced by the thickness of organic layers as well as the device structures. It is believed that organic layer thickness is a strong function of materials' exciton diffusion lengths. The thickness of the organic layer employed in the fabricated photodiode is 100 A or less. However, the fabricated devices with thin organic layer showed poor performance in terms of saturation current and breakdown voltage. As a result, new device structures have been proposed to overcome the problems. Stacking structure double heterojunction (SDH) and novel comb-like structure single heterojunction (CSH) device configurations have shown a substantial improvement in both electrical and optical parameters. There is at least 3 times enhancement in photocurrent and 10 times increase in external quantum efficiency for photodiodes employing CSH device structure and 100 A organic layer. Improvements in saturation current and breakdown voltage have also been observed. In addition, responsivity measurements in CSH devices have yielded a 7 times improvement. Furthermore, the carrier lifetime of the photodiode is estimated to be around 1 microsecond from the temporal response measurements. The combined effect of thin organic layers and new device structures leads to an overall improvement in device performance.
8
Hoogland, J. S. "Properties of low molecular weight food surfactants". Thesis, University of Bristol, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333908.
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9
Amer, Ismael. "Molecular weight effects on crystallization of polypropylene". Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6649.
Testo completoAbstract (sommario):
Thesis (PhD)--University of Stellenbosch, 2011.ENGLISH ABSTRACT: The crystallization of polyolefins is an important parameter in determining the properties of such materials. The crystallization phenomenon generally depends on the molecular symmetry (tacticity) and molecular weight of the material. In this study, a series of polypropylenes was prepared using heterogeneous MgCl2-supported Ziegler catalysts with two different external donors, diphenyldimethoxysilane (DPDMS) and methyl-phenyldimethoxysilane (MPDMS), and two different homogeneous metallocene catalysts, racethylene- bis(indenyl) zirconium dichloride, Et(Ind)2ZrCl2 (EI), and rac-ethylene-bis(4,5,6,7- tetrahydro-1-indenyl) zirconium dichloride, Et(H4Ind)2ZrCl2 (EI(4H)). Molecular hydrogen was used as terminating agent. In order to establish a correlation between the molecular weight and the crystallization of these polymers, fractionation of the materials according to crystallizability was performed by means of temperature rising elution fractionation (TREF). This affords the opportunity of blending materials of different molecular weights but similar symmetry. These materials were characterized using various analytical techniques: differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), 13C nuclear magnetic resonance spectroscopy (13C-NMR), high temperature gel permeation chromatography (HT-GPC) and Fourier-transform infrared spectroscopy (FT-IR). DSC was used to study the bulk crystallization of different polypropylene blends, most of which showed only one melting peak. The latter is usually associated with a high degree of cocrystallization. Turbidity analysis of the different polypropylene polymers, obtained using solution crystallization analysis by laser light scattering (SCALLS), provided good crystallization information – similar to that provided by crystallization analysis fractionation (CRYSTAF) and TREF. It was also possible to differentiate between polypropylenes with similar chemical structure but different tacticity and molecular weight. SCALLS results also showed that the blends of different isotactic polypropylene polymers were miscible and cocrystallization had occurred, whereas, the blends of syndiotactic polypropylene and different isotactic polypropylenes were not miscible and some interaction between phases had occurred. Optical microcopy (OM) and scanning electronic microscopy (SEM) were used to study the morphological properties of different isotactic polypropylenes. Results revealed a welldefined and large spherulitic morphology of mixed a1 (disordered) and a2 (ordered) crystal form structures. OM and SEM images also clearly showed an effect of molecular weight and tacticity on the crystal structure of the different polypropylene samples. Finally, various homopolymers and blends were studied to investigate the effect of molecular weight on the mechanical properties of these materials. This was done using microhardness testing and dynamic mechanical analysis.
AFRIKAANSE OPSOMMING: Die kristallisasie van poliolefiene is ‘n belangrike faktor wat die eienskappe van hierdie tipe materiale bepaal. In die algemeen hang kristallisasie af van die molekulêre simmetrie (taktisiteit) en molekulêre massa van die materiaal. ‘n Reeks polipropilene is berei deur gebruik te maak van heterogene MgCl2-ondersteunde Ziegler-kataliste met twee verskillende elektron donors, difenieldimetoksisilaan (DPDMS) en metielfenieldimetoksisilaan (MPDMS), en twee verskillende homogene metalloseenkataliste, rac-etileen-bis(indeniel) sirkoniumdichloried, Et(Ind)2ZrCl2 (EI), en rac-etileen-bis(4,5,6,7-tetrahidro-1-indeniel) sirkoniumdichloried, Et(H4Ind)2ZrCl2 (EI(4H)). Molekulêre waterstof is gebruik as termineringssagent. Ten einde ‘n verband te bepaal tussen die molekulêre massa en kristallisasie van hierdie polimere is hulle gefraksioneer op die basis van hulle kristallisseerbaarheid deur gebruik te maak van temperatuurstyging-elueringsfraksionering (TREF). Deur hierdie tegniek verkry ons materiale van verskillende molekulêre massa maar met dieselfde taktisiteit wat ons kan vermeng. Verskeie tegnieke is gebruik om hierdie materiale te karakteriseer: differensiële skandeerkalorometrie (DSC), wyehoek X-straal diffraksie (WAXS), 13C-kernmagnetiese resonansspektroskopie (13C-KMR), hoë-temperatuur gelpermeasiechromotagrafie (HT-GPC) en Fourier-transform-infrarooispektroskopie (FT-IR). DSC is gebruik om die vaste-toestand kristallisasie van verskeie vermengde polipropilene te bestudeer., en net een smeltpunt is in meeste gevalle waargeneem. Laasgenoemde word gewoonlik verbind met ‘n hoë mate van kokristallisasie. Oplossingkristallisasie analise, dmv laserligverstrooiing (SCALLS), is gebruik om die turbiditeit van die verskillende polipropileen kopolimeervermengings te bepaal. Goeie inligting aangaande die kristallisasie in oplossing – soortgelyk aan dié wat dmv die kristallisasie-analise-fraksioneringstegniek (CRYSTAF) en TREF bepaal is, is verkry. Dit was ook moontlik om te onderskei tussen polipropilene met soortgelyke chemiese strukture maar verskillende taktisiteit en molekulêre massas. SCALLS data het ook getoon dat die vermengings van verskeie isotaktiese polipropileen polimere versoenbaar was en dat kokristallisasie plaasgevind het, terwyl vermengings van sindiotaktiese polipropileen en verskeie isotaktiese polipropilene nie versoenbaar was nie en dat ‘n mate van fase-skeiding plaasgevind het. Optiese mikroskopie (OM) en skandeer-elektronmikroskopie (SEM) is gebruik om die morfologiese eienskappe van verskillende isotaktiese polipropilene te bepaal. Goed gedefineerde en groot sferulitiese morfologie van gemengde a1 (onordelike struktuur) en a2 (ordelike struktuur) kristal-strukture is waargeneem. OM en SEM beelde het ook gewys dat molekulêre massa en taktisiteit ‘n effek het op die kristalstruktuur van die verskillende polipropileenmonsters. Laastens is die meganiese eienskappe van ‘n verskeidenheid homopolimere en vermengde materiale bestudeer, deur gebruik te maak van mikro-hardheid metings en dinamiesmeganiese analise (DMA).
10
Forde, Janice. "The molecular biology of the high molecular weight glutenin subunits of wheat". Thesis, Rothamsted Research, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.352836.
Testo completo
11
Tate, Kenneth Roy. "Extrusion and orientation of higher molecular weight polyethylenes". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1992. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ27807.pdf.
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12
Hettiarachchi, Rohan Jagath Kumara. "Venous thromboembolism, cancer and low molecular weight heparin". [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2000. http://dare.uva.nl/document/84386.
Testo completo
13
Roberts-Thomson, Peter John. "Low molecular weight IgM in health and disease /". Title page, index and abstract only, 1987. http://web4.library.adelaide.edu.au/theses/09MD/09mdr648.pdf.
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14
Liu, Nannan 1973. "Molecular weight distribution of long chain branched polyethylene". Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=79248.
Testo completoAbstract (sommario):
To fully understand the properties of Long Chain Branched Metallocene Polyethylene (LCB mPE), we need to understand its molecular structure and Molecular Weight Distribution (MWD). Gel Permeation Chromatography (GPC) is the most important and widely applied technique to measure the MWD. In this analytical technique, polymer molecules are fractionated by their hydrodynamic volume (i.e. the sizes of polymer molecules in dilute solution). This work is focused on the simulation of GPC for the MWD of LCB mPE.The polymerization reaction mechanism of LCB mPE provides a method to simulate the generation of LCB mPE molecules thus allowing the development of a statistical model of the structure and molecular weight distribution of LCB mPE by previous researchers. This statistical model gives a theoretical MWD. In this work after simulating the generation of one million LCB mPE molecules, we calculate the sizes (i.e. radii of gyration) of molecules at both theta and good solvent conditions to obtain the molecular size distributions. Then we simulate the fractionation in GPC and the different GPC detector responses to obtain simulated GPC MWDs. The simulated MWDs are compared to real GPC results provided by the Dow Chemical Company. We analyze the performance of GPC for long chain branched polyethylene and relate the results to the theoretical MWD.
15
Wood-Adams, Paula. "Determination of molecular weight distribution from rheological measurements". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=22683.
Testo completoAbstract (sommario):
An important characteristic of a polymer is its molecular weight distribution (MWD). The MWD affects both the processing and solid state performance properties of polymeric materials. Currently the analytical method for evaluating MWD involves the use of gel permeation chromatography (GPC). This is a labor and time intensive procedure, with the accuracy of the results depending strongly on the skill and experience of the equipment operator. Furthermore, GPC is not sensitive to small amounts of high molecular weight material that can have an important effect on processing and product properties. Thus GPC is far from ideal as a tool for industrial quality control. It is known that the rheological properties depend on the MWD, and it has been proposed that complex viscosity data be used to infer the MWD for commercial polymers. There has been some degree of controversy as to whether this is feasible, but recent results of Shaw, Tuminello and their coworkers indicate that for linear polymers this is, in theory, possible. However limitations in the accessible range of frequency, as well as inevitable experimental errors pose serious barriers to the use of such a procedure. We have investigated the severity of these baniers and have shown that within certain, reasonable constraints complex viscosity data can be used to infer a realistic MWD and that this procedure could be used for routine quality control in a production facility.
16
Kronholm, David Franklin 1967. "Molecular weight growth pathways in fuel-rich combustion". Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8996.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2000.Includes bibliographical references.
Polycyclic aromatic hydrocarbons (P AH) and soot are formed when a hydrocarbon fuel is oxidized under fuel-rich conditions. The distinction between what constitutes the largest P AH molecule and the smallest soot particle is arbitrary; the formation processes of both can be placed under the heading of molecular weight growth. Evidence exists for the carcinogenicity of many P AH molecules. Soot is used as a component of dyes and as an additive to rubbers as well as being an undesirable atmospheric pollutant. Both are emitted from many typical combustion processes such as diesel engines, wood fires, furnaces, etc. Though the area has received much attention, the fundamental chemical mechanisms for formation of both P AH and soot are still uncertain. Much debate has centered on the identity of the soot surface growth reactant, in particular whether the dominant surface growth reactant is P AH or acetylene. Though several models of soot formation exist, none has demonstrated through comparison to experimental data a thorough knowledge of the fundamental chemical processes of soot formation. The goal of this research was to further the understanding of these fundamental chemical processes. Since the chemistry of P AH and soot are intertwined, PAH was a necessary subcomponent of the soot formation research. The research was accomplished by obtaining soot particle size distribution data for the jet-stirred reactor/ plug-flow reactor (JSR/PFR), development of kinetics modeling methods, and the development of a kinetics model of soot formation. The JSR/PFR has been used extensively in the past to investigate P AH and soot formation, providing much data for concentrations of light-gas species, P AH, and soot under various conditions of equivalence ratio, temperature, and PFR additives. No experimental data have been obtained for soot particle size distribution in the JSR/PFR, so a study was undertaken here to obtain the soot particle size distributions for two conditions previously studied by Marr, premixed atmospheric ethylene combustion at equivalence ratio 2.2 and temperatures of 1520 K and 1620 K. Thermophoretic sampling was used to obtain soot samples for transmission electron micrograph analysis. Software was written and used to obtain soot particle sizes from electron micrographs. The chemical environment in a fuel-rich flame consists of many hundreds of species and thousands of chemical reactions. To isolate particular portions of the chemistry, a calculational technique was developed, data incorporation, that replaces chosen portions of the chemistry in kinetics models with functions of data concentrations. This technique was then used to isolate the process of P AH molecular weight growth and soot nucleation through the use of a discrete sectional model, and rate coefficients for hydrogen-atom abstraction, acetylene-addition, and PAH radical addition to PAH were obtained by comparisons to data from Marr for the 1620 K condition described above and the same condition with naphthalene injection into the PFR. The data incorporation technique was then used to expand the discrete sectional model to include sections describing soot, and the experimental soot size distribution data described above was used with previously available PFR data to obtain values for rate coefficients of PAHaddition to soot and coagulation of soot particles. Five PFR conditions were used to develop the soot formation model in these calculations, and the dominant mechanisms of soot formation present under these conditions appear to be present in the model. Quantitative agreement is obtained to all of the available data, including simultaneous agreement of soot mass and particle size, without significant deviation in the rate coefficients required to obtain agreement. Calculations were performed using both PAH and acetylene as the dominant soot surface growth reactant. It was found that P AH had far more consistent rate coefficient values (constant to within a factor of 4) than acetylene ( constant to within a factor of 59) to describe the data for all of the conditions. An analysis of the above five sets of conditions in the PFR, an additional three for the PFR, and three for premixed one-dimensional flames of acetylene, ethylene, and benzene, for which concentrations of acetylene, P AH. and soot, and in the case of the one-dimensional flames, soot particle size data, were available, were analyzed with the aim of understanding the dominant characteristics of the soot surface growth reactant. Soot mass growth rates were calculated for all of the conditions, and deviate markedly between the PFR and one-dimensional flames. Soot growth rate increases and oscillates in the PFR and sharply declines in the one-dimensional flames in the region of soot growth after initial particle inception. Under all of these conditions, PAH show the characteristics required of the dominant surface growth reactant: increases and oscillations in the PFR and sharp declines in the one-dimensional flames. For acetylene to be the dominant surface growth reactant, anomalous behavior of acetylene-suot reactivity would be required that cannot be explained by soot aging or radical intermediates. This leads to the observation that the long-held notion of declining soot reactivity in premixed one-dimensional flames similar to the ones studied here is a result of variations in the PAH intermediates and not a real phenomenon in the region after soot particle inception. An approximate method of uncertainty analysis of kinetics models was used to place an uncertainty bound of a factor of 3 on the rate coefficient parameters calculated. The approximate method was compared to more precise techniques and used to show that the uncertainty of concentration predictions with PAH kinetics models is of very large magnitude. The approximate uncertainty analysis technique was also used to show that the data incorporation technique reduces the uncertainty in calculated rate parameters by over two orders of magnitude. A kinetics model reduction algorithm was developed and implemented to reduce a PAH kinetics model fro.n 722 reactions and 187 species to 93 reactions and 52 species, maintaining naphthalene conc1;;ntration to within 9% of the original model. This technique was also used by Dinaro to redm:e a benzene oxidation model from 545 to 41 reactions for use in super-critical water oxidation applications.
by David Franklin Kronholm.
Ph.D.
17
Pawlus, Sebastian, Yoshi Hayashi, Kunal Kumar e Alexei P. Sokolov. "Dynamic crossover in polymers, role of molecular weight". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194211.
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Pawlus, Sebastian, Yoshi Hayashi, Kunal Kumar e Alexei P. Sokolov. "Dynamic crossover in polymers, role of molecular weight". Diffusion fundamentals 6 (2007) 80, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A13209.
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Karanfilov, Christopher. "ION IMPLANTATION OF ULTRA-HIGH MOLECULAR WEIGHT POLYETHYLENE". The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243981285.
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Weidknecht, Marcia E. "Mechanical Properties of Very High Molecular Weight Polyisobutylene". University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1404846490.
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21
Mauron, Thomas. "Influence of low molecular weight heparin and low molecular weight dextran sulfate on the inhibition of coagulation factor XIa by serpins /". Bern : Hämatologisches Zentrallabor der Universität Inselspital, 1998. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
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22
Ghielmi, Alessandro. "Molecular weight distribution and gel formation in emulsion polymerization /". [S.l.] : [s.n.], 1999. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=13436.
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23
Tups, Alexander. "Molecular and neuroendocrine determinants of seasonal body weight regulation". [S.l.] : [s.n.], 2005. http://archiv.ub.uni-marburg.de/diss/z2006/0063.
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24
Fernández, Fleischhaver Daniel Hugo. "Discovery and characterization of small molecular weight metallocarboxypeptidase inhibitors". Doctoral thesis, Universitat Autònoma de Barcelona, 2009. http://hdl.handle.net/10803/3623.
Testo completoAbstract (sommario):
Las hidrolasas son enzimas que catalizan la ruptura del enlace amida o peptódico, y por lo tanto son denominadas también proteasas o peptidasas. Las proteasas constituyen cerca del 2 % del genoma humano, lo que representa unos 600 productos génicos. De acuerdo con el residuo catalóticamente activo, existen seis grandes grupos de peptidasas. En este trabajo nos centraremos en la familia M14 de peptidasas, también denominadas metalocarboxipeptidasas (CPs) debido a que su actividad catalótica reside en el ion zinc presente en el sitio activo de la enzima. En el genoma humano, se han identificado al menos 26 genes que codifican carboxipeptidasas. Las peptidasas de la familia M14 que actúan en el tracto gastrointestinal son las principales metaloproteasas responsables de la obtención de aminoácidos libres de la proteína de la dieta. En otros compartimientos corporales, las CPs pueden llevar a cabo tareas especializadas y altamente reguladas como ser la maduración de neuropéptidos, citokinas y hormonas peptódicas. En algunos casos, una actividad catalótica fuera de control puede conducir a enfermedades. Cada vez existe una mayor evidencia experimental que demuestra la actividad carboxipeptidasa en procesos como la pancreatitis aguda, la diabetes, la inflamación, la fibrinólisis y el cáncer. A pesar de ciertos avances en algunos aspectos, la actividad específica de las CPs es pobremente conocida. Además, las carboxipeptidasas son blancos terapéuticos interesantes para el desarrollo de fármacos, y por lo tanto se ha decidido emplear una aproximación multi-disciplinaria para la identificación y caracterización de nuevas moléculas de bajo peso molecular capaces de interferir la actividad carboxipeptidasa. Así, en este trabajo se han combinado modernas herramientas computacionales, screening in vitro, modelado molecular y cristalografía de rayos X con el fin de obtener nuevas entidades quφmicas como base para el desarrollo de fármacos. Con base en herramientas computacionales, aplicando el método de Optimal Docking Areaö, se han caracterizado sitios de unión proteína-proteína y proteína-ligando en la superficie de las peptidasas de la familia M14. A partir de aquí, se identificó una nueva clase de compuestos químicos capaces de explotar las diferencias existentes entre enzimas de la familia por unión a regiones hidrofóbicas. Otros inhibidores fueron identificados mediante un screening in silico de grandes colecciones de compuestos. Ensayos in vitro demostraron que los compuestos líderes inhibieron de manera potente a las carboxipeptidasas blanco con otras características interesantes como la posibilidad de coordinación del ion zinc catalítico por intermedio de un anillo oxadiazol. A través de una colaboración con el Departamento de Química Orgánica se obtuvieron y caracterizaron nuevos compuestos químicos con conectividades atómicas novedosas que, inesperadamente, demostraron ser potentes inhibidores de carboxipeptidasas. Una clase adicional de molécula de bajo peso molecular caracterizada corresponde a inhibidores que se unen covalentemente al enzima blanco. En este caso, se logró obtener la estructura tridimensional del complejo a resolución atómica mediante cristalografφa de rayos X, lo que ha permitido el dise±o basado en la estructura de una nueva generación de compuestos. Basados en otros datos de cristalografía de rayos X y análisis computacional, se ha revisado y ampliado el mecanismo de acción catalítica de las peptidasas de la familia M14 a partir de una nueva forma cristalina de CPB a alta resolución. En conjunto, nuestro trabajo ha permitido la obtención de nuevas moléculas líderes de bajo peso molecular que podrían servir como base para futuros desarrollos en el diseño de fármacos y agentes de diagnóstico o imaginería dirigidos a metalocarboxipeptidasas fisiológicamente activas.Hydrolases are enzymes catalyzing the breakdown of the amide or peptide bond, and are therefore called proteases or peptidases as well. In the human genome, proteases made up about 2% of the genome, or about 600 gene products. There are six major groups of peptidases according to the catalytic residue. In our work we focused on the M14 family of peptidases, also called metallocarboxypeptidases (CPs) because of their catalytic activity hinges on the zinc ion present in the active site of the enzyme. In the human genome there are identified at least 26 genes encoding for CPs. M14 peptidases in the gastrointestinal tract are the main metalloproteases responsible of the liberation of free aminoacids from the protein content of the diet. In other compartments of the body, CPs may perform specialized and tightly controlled tasks such as neuropeptide, cytokine and hormone maturation. In some instances an imbalance in their activity leads to disease states in man. Increasing evidence shows carboxypeptidase involvement in acute pancreatitis, diabetes, inflammation, fibrinolysis and cancer. Although some aspects have become clearer, much of their activity remain poorly understood. Besides, carboxypeptidases are interesting targets for drug development, and therefore we pursued a multidisciplinary approach to identify and characterize novel small molecular weight compounds able to interfere carboxypeptidase activity. In this work we combined modern computational tools, in vitro screening, molecular modelling and X-ray crystallography to obtain new chemical entities useful as scaffolds for drug design. Based on a bioinformatics tools, the Optimal Docking Area method, we identified protein-protein and protein-ligand binding sites over the surface of M14 peptidases. This knowledge was employed to find out a new class of small molecular weight inhibitors which exploit the differential binding provided by hydrophobic patches. A further class of inhibitors was identified from in silico screening of collections of compounds. In vitro analysis revealed that the leads were potent inhibitors against the target proteases with interesting features like an oxadiazole zinc-chelating moiety. Compounds obtained from the Organic Chemistry Department were also screened, and unexpectedly, afforded some good inhibitors with unprecedented atomic bonding. One further class involved inhibitors that attach covalently to the target enzyme. In this case the structure of the complex obtained at high resolution by X-ray crystallography allowed the structure-guided design of new generation of compounds. The catalytic mechanism of M14 peptidases was also revisited based on our crystallographic and computational analysis of a new CPB crystal form at high resolution. Overall, our study provided new lead small molecular weight inhibitors which can be the foundation for further developments in the design of drugs and bioimaging or diagnostic agents targeted to physiologically-relevant metallocarboxypeptidases.
25
Krywko, William P. "Modelling morphology and molecular weight development in emulsion homopolymerization". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ36045.pdf.
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Adebekun, Aderinola Kolawole. "On-line estimation and control of molecular weight distribution". Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/11765.
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Kuo, Betsy P. "Narrowing the molecular weight distribution of linear alcohol ethoxylates". Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/11773.
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28
Gao, Ping. "Swelling and drawing behaviour of ultrahigh molecular weight polyethylene". Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335714.
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Ding, Yifu. "Influence of Molecular Weight and Architecture on Polymer Dynamics". University of Akron / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=akron1115933800.
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Chen, Qiang. "The major chloroplast low molecular weight heat shock protein". Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185849.
Testo completoAbstract (sommario):
The goal of this dissertation is to provide information critical for understanding the function of the major chloroplast LMW HSP. The results of this research show that the production of a nuclear-encoded, chloroplast LMW HSP is a highly conserved event in the plant HS response, and that the HSP itself is highly homologous in divergent plant species. Three major conserved regions were identified in the chloroplast LMW HSP. The carboxyl-terminal HS domain of the chloroplast LMW HSP is also found in cytoplasmic LMW HSPs and identifies it as a member of the superfamily of eukaryotic LMW HSPs. The amino-terminal region is unique to the chloroplast LMW HSP and is capable of forming a Met-rich amphipathic α-helix. The chloroplast LMW HSP cannot be detected at normal growth temperatures, but accumulates dramatically in both leaves and roots during HS. The chloroplast LMW HSP is a stable protein with a half-life of approximately 52 h. In the chloroplast, the majority of PsHSP21 is localized in the soluble protein fraction. In its native state, PsHSP21 exists in a 200 kDa particle as is observed for cytoplasmic LMW HSPs. However, unlike the cytoplasmic LMW HSPs, the PsHSP21-containing particles do not aggregate into heat shock granules even under severe, abrupt HS conditions. The formation of the PsHPS21-containing particle can be replicated in isolated chloroplasts, but the chloroplasts must be from heat stressed plants. The protein sequence homology and the similar native structure of the LMW cytoplasmic and chloroplast HSPs suggests they perform similar functions in different cellular compartments. I propose that the 200 kDa particle is the functional form of PsHSP21. Furthermore, the chloroplast LMW HSP performs functions in all types of plastids similar to those of the cytoplasmic LMW HSPs, but with unique substrates within the special environment of plastids. This study provides the first information regarding the expression and structure of the chloroplast LMW HSP. Since the chloroplast contains only a single major LMW HSP, this study also provides the basis for developing a simple model system for studies of the function of all members of the ubiquitous LMW HSP family.
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Song, Yang. "OXIDATIVE DEPOLYMERIZATION OF LIGNIN TO LOW MOLECULAR WEIGHT AROMATICS". UKnowledge, 2019. https://uknowledge.uky.edu/chemistry_etds/114.
Testo completoAbstract (sommario):
To date, most lignocellulosic biorefinery strategies have focused on optimizing conversion of cellulose to ethanol, leaving lignin as an underutilized biomass constituent. Lignin is engineered by nature with the intent to protect plants from chemical and biological attack; this leaves lignin with high structural irregularity and recalcitrance, rendering conversion of the lignin macromolecule to valuable products particularly challenging. Nevertheless, given that the economics of cellulosic ethanol production are strongly dependent on the value that can be obtained for the lignin co-product, the successful valorization of lignin is a crucial step in the transition towards a bio-based economy.
This thesis focuses on lignin depolymerization using oxidative methods, specifically, the oxidation and cleavage of the β-O-4 linkage. Heterogeneous catalysis in this case is more desirable than homogenous catalysis as the catalyst easily recovered, and it is better suited for industrial applications. Initially, layered double hydroxide (LDH) supported gold nanoparticles were characterized and screened in the oxidation of various lignin model compounds using molecular oxygen, leading to the discovery of an Au/Li-Al LDH heterogeneous catalyst active for oxidative cleavage of the β-O-4 linkage. The Au/Li-Al LDH catalyst was then applied to oxidatively depolymerize Indulin AT kraft lignin and γ-valerolactone (GVL) extracted lignin, high yields of monomers being observed when the oxidized lignins underwent subsequent base-catalyzed hydrolysis. Thereafter, different literature oxidative lignin depolymerization methods were tested on kraft lignin and GVL lignin, and the results compared to the Au/Li-Al LDH catalyst (coupled with hydrolysis) system to determine the most effective oxidative depolymerization method.
32
Chang, Natasha Anna 1974. "The effect of molecular orientation on the wear of ultra-high molecular weight polyethylene". Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/46240.
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Brás, Ana Rita Elias. "Influence of constraining and confinement in the molecular mobility of low molecular weight materials". Doctoral thesis, FCT - UNL, 2009. http://hdl.handle.net/10362/2670.
Testo completoAbstract (sommario):
Dissertation presented to obtain a Ph.D. Degree in Chemical PhysicsDespite the importance that the glassy state has nowadays, the transition from liquid to the glass, glass transition, still remains a matter of debate which constitutes one of the great condensed matter physics challenges. Since this fact is closely related to the cooperativity dynamics, the study of this phenomenon in glass-forming liquids under confinement in the nanometer scale, has recently emerged as a strategy to clarify factors such as the existence of an inherent length scale of the cooperative dynamics that determines the glass transition temperature. In this context, this thesis represents an additional contribution to the study of molecular dynamics of glass-forming liquids under confinement in nanoporous inorganic materials. As target compounds the liquid crystal E7 and the drug Ibuprofen were selected. Since the first exhibit various transitions makes it more sensitive to perturbations and thus appears as the ideal candidate to evaluate confinement effects. The study of ibuprofen is of particular interest because confinement emerges as a method of stabilizing the amorphous phase that is mostly important in pharmaceutical applications. Dielectric Relaxation Spectroscopy(DRS) is the main technique used to obtain detailed information about the molecular mobility in a wide range of frequencies (10-2-109Hz) (Chapter I and II). The first part of the thesis is devoted to the characterization of the two target compounds in the bulk state. The combination of DRS with the specific heat spectroscopy allowed to determine which of the E7 observed relaxation processes (a process in the isotropic phase and two processes in the nematic phase: δ and tumbling) is responsible for the glass transition temperature Tg (tumbling process). Detailed studies of ibuprofen molecular mobility in the liquid, supercooled liquid and glassy states are also presented in this chapter, where four relaxation processes are detected: two secondary processes (γ and β), the cooperative process related to Tg (α ) and the Debye process (D), probably related to the hydrogen bonding dynamics. This study was preceded by an optimization of the conditions to obtain amorphous Ibuprofen which is a crystal in its natural state (Chapter III). In the next chapter (Chapter IV), the molecular dynamics of E7 confined to untreated and phospholipid lecithin treated rigid inorganic membranes with 20 nm pore diameter was evaluated. It was found that both the liquid crystal alignment, as well as the dynamics is influenced by confinement and treatment of the surface pores. Additionally, E7 was further studied confined to the mesoporous materials MCM-41 and SBA-15 type, 100% silica composition and pore size between the 2.8 and 6.8 nm. A multiplicity of relaxation processes was revealed by DRS, including the modes already observed in the bulk E7. In addition, two
Fundação para a Ciência e Tecnologia (FCT),financial support by means of the PhD grant SFRH/BD/23829/2005
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Hedge, P. J. "Molecular genetic approaches to the structure of a high molecular weight penicillin-binding protein". Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372053.
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Benner, Susanne. "Freisetzung von Bradykinin aus High Molecular Weight Kininogen durch Plasmakallikrein /". [S.l.] : [s.n.], 1994. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10910.
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Rodríguez, Seco Cristina. "Low-Molecular Weight Semiconductors for Organic and Perovskite Solar Cells". Doctoral thesis, Universitat Rovira i Virgili, 2019. http://hdl.handle.net/10803/667660.
Testo completoAbstract (sommario):
Actualment, les fonts d'energia renovables estan atraient molta atenció degut a l'impacte negatiu que els combustibles
fòssils estan causant al planeta. Les tecnologies basades en les cel·les fotovoltaiques són una alternativa sostenible
per cobrir la demanda energètica mundial.
El principal objectiu d'aquest treball és el disseny i la síntesis de noves molècules per tal de reemplaçar els polímers
habitualment utilitzats com a molècules captadores de llum en cel·les solars orgàniques i el spiro-OMeTAD usat com a
transportador de buits (HTM per les sigles en anglès "hole transporting material") en dispositius solars de perovskita.
D'una banda, els polímers són coneguts per ser bons transportadors de buits, posseir una elevada solubilitat i una
bona habilitat per a la formació de capes, però entre els diferents lots existeix una baixa reproductibilitat degut a la
seva síntesi complexa. D'altra banda, el spiro-OMeTAD és la molècula que millor reproductibilitat i eficiència presenta
en cel·les solars de perovskita. No obstant això, la seva síntesi complexa i d’alt cost impedeix la possibilitat d'escalat a
nivell industrial.
Per tal de solucionar aquests problemes, aquesta tesi s'ha enfocat en el disseny, síntesi i caracterització d'un conjunt
de molècules petites de baix pes molecular per a la seva aplicació en aquests dispositius.Actualmente, las fuentes de energía renovables están atrayendo mucha atención debido al impacto negativo que los combustibles fósiles están causando al planeta. Las tecnologías basadas en las celdas fotovoltaicas son una alternativa sostenible para cubrir la demanda energética mundial. El principal objetivo de este trabajo fue el diseño y la síntesis de nuevas moléculas que reemplacen los polímeros comúnmente utilizados como moléculas captadoras de luz en celdas solares orgánicas y el spiro-OMeTAD usado como transportador de huecos (HTM por sus siglas en inglés “hole transporting material”) en dispositivos solares de perovskita. Por una parte, los polímeros son conocidos por ser buenos transportadores de huecos, su alta solubilidad y su favorable habilidad en la formación de capas, pero tienen muy poca reproducibilidad entre distintos lotes. Por otra parte, el spiro-OMeTAD es la molécula que mejor reproducibilidad y eficiencia presenta en celdas solares de perovskita. Sin embargo, su síntesis compleja y de alto coste impide la posibilidad de escalado a nivel industrial. Con el fin de solucionar estos problemas, esta tesis se ha enfocado en el diseño, síntesis y caracterización de un conjunto de moléculas pequeñas de bajo peso molecular para su aplicación en dichos dispositivos
Nowadays, renewable energy sources are attracting a lot of attention due to the undesired environmental impact the fossil fuels are causing to the Earth. Solar cells technologies are a sustainable alternative to the increasing world energy demand. The main aim of this work was to design and synthetize novel molecules that could replace the polymers widely used as absorbers in organic solar cells and spiro-OMeTAD used as a hole transporting material (HTM) in perovskite solar cells. On the one hand, polymers are known for their good hole transporting properties, high solubility and good film forming abilities but they have a poor batch-to-batch reproducibility. Furthermore, spiro-OMeTAD is the best molecule to achieve reproducible and highly efficient perovskite solar cells. However, its complex and expensive synthesis and purification hinder its usage in industrial scale photovoltaics. In order to overcome these problems, the rational design, synthesis and characterization of a variety of small molecules for both applications have been on a focus of this thesis.
37
Burger, Nicolaas Daniel Lombard. "Failure analysis of ultra-high molecular weight polyethyelene acetabular cups". Pretoria : [s.n.], 2005. http://upetd.up.ac.za/thesis/available/etd-12142006-134036.
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Zhang, Zhijie. "A study of ultra-high-molecular-weight polyethylene, UHMWPE, foams". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ60758.pdf.
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Roukema, Mees. "High-speed spinning of ultra-high molecular weight polyethylene fibres". [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 1991. http://irs.ub.rug.nl/ppn/291241077.
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Taidi, Behnam. "Control of the molecular weight of bacterial poly(3-hydroxybutyrate)". Thesis, University of Hull, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262472.
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Sosa, Oscar Abraham. "Microbial cycling of marine high molecular weight dissolved organic matter". Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/104332.
Testo completoAbstract (sommario):
Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Civil and Environmental Engineering; and the Woods Hole Oceanographic Institution), 2015.Cataloged from PDF version of thesis.
Includes bibliographical references.
Microorganisms play a central role mediating biogeochemical cycles in the ocean. Marine dissolved organic matter (DOM) - a reservoir of organic solutes and colloids derived from plankton is a major source of carbon, nutrients, and energy to microbial communities. The biological transformation and remineralization of DOM sustains marine productivity by linking the microbial food web to higher trophic levels (the microbial loop) and exerts important controls over the cycles of carbon and bioessential elements, such as nitrogen and phosphorus, in the sea. Yet insight into the underlying metabolism and reactions driving the degradation of DOM is limited partly because its exact molecular composition is difficult to constrain and appropriate microbial model systems known to decompose marine DOM are lacking. This thesis identifies marine microorganisms that can serve as model systems to study the metabolic pathways and biochemical reactions that control an important ecosystem function, DOM turnover. To accomplish this goal, bacterial isolates were obtained by enriching seawater in dilution-to-extinction culturing experiments with a natural source of DOM, specifically, the high molecular weight (HMW) fraction (>1 kDa nominal molecular weight) obtained by ultrafiltration. Because it is relatively easy to concentrate and it is fairly uniform in its chemical composition across the global ocean and other aquatic environments, HMW DOM has the potential to serve as a model growth substrate to study the biological breakdown of DOM. The phylogeny, genomes, and growth characteristics of the organisms identified through this work indicate that HMW DOM contains bioavailable substrates that may support widespread microbial populations in coastal and open-ocean environments. The availability of ecologically relevant isolates in culture can now serve to test hypothesis emerging from cultivation-independent studies pertaining the potential role of microbial groups in the decomposition of organic matter in the sea. Detailed studies of the biochemical changes exerted on DOM by selected bacterial strains will provide new insight into the processes driving the aerobic microbial food chain in the upper ocean.
by Oscar Abraham Sosa.
Ph. D.
42
Ivy, Diane Jean. "Trends and inferred emissions of atmospheric high molecular weight perfluorocarbons". Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78537.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 115-119).
Atmospheric observations and atmospheric observation-based global emission estimates are presented for the five high molecular weight perfluorocarbons (PFCs): decafluorobutane (C 4 F 1 0 ), dodecafluoropentane (C5 F1 2 ), tetradecafluorohexane (C 6 F14 ), hexadecafluoroheptane (C 7F 16 ) and octadecafluorooctane (C8 F 18 ). Their atmospheric histories are based on measurements of 36 Northern Hemisphere and 46 Southern Hemisphere archived air samples, collected between 1973 and 2011, using two of the "Medusa" cryogenic preconcentration gas chromatography-mass spectrometry instruments, which are part of the Advanced Global Atmospheric Gases Experiment (AGAGE). A new calibration scale was prepared for each PFC, with estimated accuracies of 6.8% for C4Fi0 , 7.8% for C5F12 , 4.0% for CF 14 , 6.6% for C7FE16 and 7.9% for CF8i . Based on our observations, the 2011 globally averaged dry air mole fractions of these high molecular weight PFCs are: 0.17 parts-per-trillion (ppt, i.e., parts per 1012) for C4 F 10 , 0.12 ppt for C5 F 1 2 , 0.27 ppt for CF 1 4 , 0.12 ppt for CFE16 and 0.09 ppt for CF 18 . Newly measured infrared absorption spectra are presented for C7F 16 and CF 1 8 , and using these, their radiative efficiencies and global warming potentials (GWPs) are estimated. We find that the radiative efficiency of C8 F 18 at 0.57Wm- 2 ppb-' is similar to that of trifluoromethyl sulfur pentafluoride's (SF 5 CF 3 ), which has the highest radiative efficiency of any known atmospheric species (Forster et al., 2007). Using their radiative efficiencies, the 2011 observed globally averaged atmospheric mole fractions of the above five high molecular weight PFCs combine to contribute a global average radiative forcing of 0.35 mW m-2, which is 6% of the total anthropogenic PFC radiative forcing (Montzka et al., 2011; Oram et al., 2012). Global emissions for C4 Fio, C5F 12 , C6 F 14 , C7 F 16 and CF 18 were estimated from the observations using a 3-dimensional chemical transport model and a Bayseian inverse method that included a constraint on the annual growth rate of their emissions, consistent with the knowledge of the relevant industries emitting them (Rigby et al., 2011). The derived so-called "top-down" emission estimates show that global emission rates were largest in the 1980s and 1990s for C4 F 10 and C5 F 12 and in the 1990s for C6F 14 , C7F16 and C8F1 . After a subsequent decline, emission rates have remained relatively stable, within ±20 % year-to-year variation, for the last 5 years. Using their calculated 100-year time horizon GWPs, the high molecular weight perfluorocarbons studied here contributed up to 15.4 % of the total PFC emissions expressed in carbon dioxide (C0 2)-equivalents in 1997 and 6 % of the total PFC emissions in 2009. Furthermore, we compare our atmospheric observation-based global emissions to the available so-called "bottom-up" inventories, which are based on production information and end usage. Bottom-up emission estimates are available from the Emission Database for Global Atmospheric Research version 4.2 (EDGARv4.2) for C4F1o, C5 F1 2, C6 F 1 4 and C7F16 , and emission inventories of C4Fio, C5 F1 2 and C6 F14 are also reported to the United Nations' Framework Convention on Climate Change (UNFCCC) by Annex 1 countries that have ratified the Kyoto Protocol (European Commission, Joint Research Centre (JRC)/Netherlands Environmental Assessment Agency (PBL), 2009; United National Framework Convention on Climate Change Secretariat, 2011). The atmospheric observation-based emission estimates are 20 times larger than EDGARv4.2 for C4F10 and over three orders of magnitude larger for C5F1 2 . In contrast, the top-down emission estimates for C6F14 largely agree with the bottom-up estimates from EDGARv4.2. Moreover, the top-down C7 F16 emission estimates are comparable to those of EDGARv4.2 at their peak in the 1990s, albeit with significant underestimation by EDGARv4.2 for the other time periods. There are no bottom-up emission estimates for C8Fi8 , thus the emission rates reported here are the first for this gas. In general, the emission inventories for C4Fio, C5F1 2 and C6F 14 reported to the UNFCCC are five to ten times lower than those estimated in this study from observations. This underreporting to the UNFCCC may be due to only Annex 1 countries reporting inventories and also that some of these countries report a total PFC mixture in C0 2-equivalents, instead of individual PFC emissions rates.
by Diane Jean Ivy.
Ph.D.
43
Boontongkong, Yot. "Orientation of channel die-compressed ultra-high molecular weight polyethylene". Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/46093.
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Cheuk, Sherwin. "Glucose and Glucosamine Derivatives as Novel Low Molecular Weight Gelators". ScholarWorks@UNO, 2008. http://scholarworks.uno.edu/td/868.
Testo completoAbstract (sommario):
Low molecular weight gelators (LMWGs) are small molecules that are capable of entrapping solvents to form a gel in organic solvents or aqueous solution. These compounds rely solely on noncovalent forces to form the fibrous networks necessary to entrap a variety of solvents. The organogels and hydrogels thus formed could have applications in a variety of fields from environmental to biological to medicinal. Carbohydrates are ideal starting materials to synthesize LMWGs, because of their natural abundance, dense chirality, and biocompatibility. D-Glucose is the most common monosaccharide and D-glucosamine is isolated from natural sources, such as crab shells. Several series of compounds were synthesized using compounds 1-3 as the starting materials. These include esters, carbamates, amides, and ureas. The structure and gelation relationship was analyzed to obtain guidelines for designing new LMWGs. Compound 1 is a simple derivative of D-glucose and its terminal alkynyl esters and saturated carbamates are effective gelators. Compound 2 is a simple derivative of D-glucosamine and its amide and urea derivatives are also effective gelators. Compound 3 is formed from the deoxygenation of D-glucose. 1OOHOOCH3OHOPh2OOHOOCH3NH2OPh3OOHOOHOPh The design, synthesis and gelation properties of several classes of sugar based low molecular organo/hydrogelators will be discussed in this thesis in chapters 2, 3, and 4. After obtaining highly effective organo/hydrogelators, potential applications of these novel molecular systems can be explored. Some preliminary study on using one of the gelator in enzyme assay has shown that it is possible to utilize the hydrogels to immobilize enzymes. However, future research can explore further on the applications of these gelators.
45
Williams, Kristopher Aaron. "Synthesis and Characterization of Monosaccharide-derived Low Molecular Weight Gelators". ScholarWorks@UNO, 2011. http://scholarworks.uno.edu/td/135.
Testo completoAbstract (sommario):
Low molecular weight gelators (LMWGs) are interesting materials whose applications are as diverse and wide ranging as their molecular structures. These materials self-assemble through the formation of non-covelent intermolecular forces and interactions to form supramolecular assemblies that trap solvent within their matrices. Because of the non-covalent nature of the forces of self-assembly, the gelation process is typically thermally reversible. In addition, low molecular weight gelators can also be modified to respond to various stimuli, such as change in pH, presence of enzymes or metal cations, or exposure to light. The design of low molecular weight gelators is often difficult, and most new classes of low molecular weight gelators are discovered by serendipity. As such, it is often useful to use structural templates in the design of LMWGs. Biomolecules, such as steroids, amino acids and peptides, and carbohydrates make excellent templates due to their inherent propensity to self assemble. A review of the current literature regarding the use of biomolecules as templates for the design and synthesis of LMWGs will be presented in chapter 1. Our research group has been active in the research of carbohydrate-based LMWGs for several years, and these results are also briefly reviewed in the related chapters. The synthesis and characterization of ester derivatives of D-galactose, D-glucose, and amide derivatives of D-glucosamine will be discussed in chapters 2-4, along with their evaluation for gelation in aqueous and organic solvents, such as hexane, ethanol, water, and aqueous DMSO or ethanol mixtures.
46
Yang, Hao. "Synthesis and characterization of sugar based low molecular weight gelators". ScholarWorks@UNO, 2012. http://scholarworks.uno.edu/td/1496.
Testo completoAbstract (sommario):
Low molecular weight gelators (LMWGs) have gained great attention over the past two decades. These compounds form self-assembled fibrous networks like micelles, cylindrical, sheets, fibers, layers and so on. The fibrous network entraps the solvent and form gel. LMWGs are interesting compounds with many potential applications in material and biomedical sciences.
Many different structures have been found to be good LMWGs. Our interests focus on the carbohydrate based LMWGs. Previously, we have found that several ester derivatives of methyl 4, 6-O-benzylidene-α-D-glucopyranoside are good gelators for organic solvents and aqueous solutions. In this study, in order to understand the structure requirement, we systematically investigated the influence of sugar head groups and the attached hydrophobic tails towards gelation. The design, synthesis and gel properties of esters, amides, ureas, carbamates which derived from sugar head groups show above will be discussed in chapter II, III, IV.
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Burger, N. D. L. (Nicolaas Daniel Lombard). "Failure analysis of ultra-high molecular weight polyethyelene acetabular cups". Thesis, University of Pretoria, 2005. http://hdl.handle.net/2263/30360.
Testo completoAbstract (sommario):
Owing to the crippling nature of arthritis, surgeons have been trying for well over a century to successfully treat this debilitating disease particularly when attacking the hip joint. In the early 1970s, Sir John Charnley started with total hip replacement as a solution to this ever-increasing problem. Many different designs were developed but all the designs revolved around a femoral stem, femoral head and acetabular component. Independent of the design, longevity of the implant remains a problem. The major cause of replacements, according to various hip registers, is due to aseptic loosening resulting from osteolysis. According to these registers, the average in-vivo life of a hip replacement is approximately 12 years. The main aim of this study was to determine the root cause of mechanical failure of the acetabular cups and to determine the origin of the excessive amount of ultra-high molecular weight polyethylene (UHMWPE) wear debris floating in the joint resulting in osteolysis. During the study, various techniques were used to investigate the acetabular components to try to establish the root cause of mechanical failure. These techniques included: 1. Visual inspection 2. Investigation making use of dye penetrant spray 3. Investigation under stereo microscope 4. Investigation making use of a scanning electron microscope 5. Electrophoresis 6. Mass-spectrometric analysis 7. Analysis of the synovial fluid on high-frequency linear-oscillation machine (SRV). The wear debris retrieved from the scar tissue surrounding the joints of a number of patients was also analysed. Apart from the obvious defects such as mechanical damage due to impingement, the main defect on which this study focuses is the wear patches found on the inside of the acetabular components. The wear areas were presented as areas where the surface layer of the UHMWPE was ripped off by adhering to the rotating femoral head. This type of failure is possible if localised overheating takes place resulting in the material either adhering to the rotating femoral head or the material being squeezed out under the prevailing pressure. Both these mechanisms were confirmed by the wear debris retrieved from the scar tissue, being either droplets of UHMWPE or whisker-like wear products. To confirm the existence of elevated temperatures the brown discolouring on the inside of the acetabular cups was analysed, making use of electrophoresis, mass-spectrometric analysis and scanning electron microscope recordings. In this part of the study, it was confirmed that localised temperatures on the bearing surface had reached at least 60°C during in-vivo service. This temperature was confirmed by inserting a thermocouple just under the surface of an acetabular cup and then measuring the temperature while in-vitro testing was taking place on a hip simulator. The wear debris as retrieved was also duplicated in laboratory experiments while the temperature on the surface of an acetabular cup was monitored. It was established that wear particles similar in shape and size were formed at temperatures in excess of 90°C. At temperatures above 50°C the UHMWPE had visually shown extensive increase in creep, indicating that at these temperatures the material softens sufficiently for this type of debris to be generated The overheating as described can also only occur if there is a lack of lubrication in the bearing couple. The synovial fluid from 12 patients was retrieved during revision surgery. This synovial fluid was then tested on a high-frequency linear-oscillation machine (Optimol SRV test machine) to determine the lubricity characteristics of the synovial fluid as retrieved. It was discovered that the load-carrying capability of the synovial fluid did not comply with the minimum requirements for a fluid to function as a lubricant. The final conclusion of this study is that excessive amounts of wear debris are generated due to the localised overheating of the bearing couple as a result of insufficient lubrication. The localised heat build-up results in excessive amounts of wear debris being generated and deposited in the joint area resulting in osteolysis.Thesis (PhD (Mechanical Engineering))--University of Pretoria, 2005.
Mechanical and Aeronautical Engineering
unrestricted
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Cobzaru, Cecilia. "Asymmetric metallocene catalysts: design of ultrahigh molecular weight polypropylene plastomers". [S.l. : s.n.], 2006. http://nbn-resolving.de/urn:nbn:de:bsz:289-vts-55721.
Testo completo
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Wernle, James David. "Micron-scale wear mechanisms in ultra high molecular weight polyethylene". Related electronic resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2008. http://wwwlib.umi.com/cr/syr/main.
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Titone, John Carlos. "Supercritical carbon dioxide sterilization of ultra-high molecular weight polyethylene". Connect to resource, 2009. http://hdl.handle.net/1811/37004.
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